Devices for resetting the time of an electronic watch ensuring some electromechanical synchronism are known from the prior art. This type of electronic watch that is to be integrated into a dashboard of a motor vehicle includes analogue display hands formed of an hour hand and a minute hand driven by a stepping motor. The stepping motor used in such electronic watches is generally formed of a magnetised rotor, a stator and a coil which when it is powered creates a magnetic field in the stator which is converted into a magnet whose polarity depends upon the direction of the current in the coil. At each pulse received from the time base, the rotor makes one step driving the gear trains and the hands of the watch in a conventional manner.
This type of electronic watch further includes a power source, time counting means operating in synchronism with the display means for sufficient powering and means for detecting insufficient power. When insufficient power is detected, the hands are stopped and the corresponding value (hours, minutes) of the counting means is then stored in non-volatile storage means.
Nonetheless, it was demonstrated within the scope of the present invention, that this synchronisation method was not sufficiently reliable over time. Indeed, when the type of stepping motor described above is not being powered, it has at least two magnetically stable positions resulting from its geometry. Thus, each time the power is insufficient, the motor stopping very often causes a loss of time information insofar as the motor is statistically not in one of the two magnetically stable positions when it stops and that following the stop it inevitably returns to one of its magnetically stable positions. Depending upon the gear reduction applied between one step of the motor and the information of one minute, the accumulation of these errors can exceed several minutes and become unacceptable for providing correct time information.
Certain prior art solutions suggest using hand position detectors for calculating and correcting this error between the actual position of the hands and that indicated in the time counting means. Such solutions are often complex and are, moreover, not necessarily very reliable.